Modular bi-directional clutch assembly

ABSTRACT

A controllable, multi-mode, bi-directional overrunning clutch assembly and a shift system are adapted for use in a power transmission device. The clutch assembly includes a first ring journalled on a first rotary member, a second ring fixed to a second rotary member, and a plurality of rollers disposed in opposed cam tracks formed between the first and second rings. The first ring is split to define an actuation channel having a pair of spaced end segments. An actuator ring is moveable between positions engaged with and released from the end segments of the first ring. The shift system includes a moveable clutch actuator which controls movement of the actuator ring for establishing engaged and disengaged clutch modes. An alternate embodiment clutch assembly includes first and second rings non-rotatably coupled to one another. A third ring is selectively engageable with a rotary component to transfer power thereto.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 10/080,420 filed on Feb. 22, 2002 which claims thebenefit of U.S. Provisional Application No. 60/287,155 filed on Apr. 27,2001.

FIELD OF THE INVENTION

[0002] The present invention relates generally to bi-directionaloverrunning clutch assemblies and, more particularly, to anactively-controlled, multi-mode, bidirectional overrunning clutchassembly used in a four-wheel drive transfer case.

BACKGROUND OF THE INVENTION

[0003] Four-wheel drive vehicles are in great demand due to the enhancedon and off road traction control they provide. In many four-wheel drivevehicles, a transfer case is installed in the drivetrain and is normallyoperable to deliver drive torque to the primary driveline forestablishing a two-wheel drive mode. The transfer case is furtherequipped with a clutch assembly that can be selectively or automaticallyactuated to transfer drive torque to the secondary driveline forestablishing a four-wheel drive mode. These “mode” clutch assemblies canrange from a simple dog clutch that is operable for mechanicallyshifting between the two-wheel drive mode and a “locked” (i.e.,part-time) four-wheel drive mode to a more sophisticatedautomatically-actuated multi-plate clutch for providing an “on-demand”four-wheel drive mode.

[0004] On-demand four-wheel drive systems are able to provide enhancedtraction and stability control and improved operator convenience sincethe drive torque is transferred to the secondary driveline automaticallyin response to lost traction of the primary driveline. An example ofpassively-controlled on-demand transfer case is shown in U.S. Pat. Nos.5,704,863 where the amount of drive torque transferred through apump-actuated clutch pack is regulated as a function of the interaxlespeed differential. In contrast, actively-controlled on-demand transfercases include a clutch actuator that is adaptively controlled by anelectronic control unit in response to instantaneous vehicular operatingcharacteristics detected by a plurality of vehicle sensors. U.S. Pat.Nos. 4,874,056, 5,363,938 and 5,407,024 disclose various examples ofadaptive on-demand four-wheel drive systems.

[0005] Due to the cost and complexity associated with suchactively-controlled on-demand clutch control systems, recent effortshave been directed to the use of overrunning clutches that can becontrolled to provide various operating modes. For example, U.S. Pat.No. 5,993,592 illustrates a pawl-type controllable overrunning clutchassembly installed in a transfer case and which can be shifted betweenvarious drive modes. U.S. Pat. No. 6,092,635 discloses ahydraulically-actuated multi-function controllable overrunning clutchassembly that is noted to be operable for use in vehicular powertransmission mechanisms. Likewise, U.S. Pat. Nos. 5,924,510, 5,951,428,6,123,183, and 6,132,332 each disclose a controllable multi-modeoverrunning clutch installed in a transfer case and which is actuatedusing an electromagnetic clutch. Accordingly, a need exists to continuedevelopment of controllable bi-directional overrunning clutch assemblieswhich provide improved structure, robust operation, and reducedpackaging for use in on-demand transfer cases.

SUMMARY OF THE INVENTION

[0006] The present invention is directed to a controllable, multi-mode,bi-directional overrunning clutch assembly and a shift system adaptedfor use in a transfer case for transferring drive torque from a primaryoutput shaft to a secondary output shaft so as to establish a four-wheeldrive mode. The clutch assembly includes a first ring journalled on afirst rotary member, a second ring fixed to a second rotary member, anda plurality of rollers disposed in opposed cam tracks formed between thefirst and second rings. The first ring is split to define an actuationchannel having a pair of spaced end segments. An actuator ring ismoveable between positions engaged with and released from the endsegments of the first ring. The shift system includes a moveable clutchactuator which controls movement of the actuator ring for establishingan on-demand four-wheel drive mode and a locked or part-time four-wheeldrive mode.

[0007] The transfer case of the present invention also includes atwo-speed gearset and a range sleeve that is moveable for establishinghigh and low-range drive connections. In such two-speed transfer cases,the shift system also functions to coordinate movement of the clutchactuator and the range sleeve to establish various combinations of speedranges and drive modes.

[0008] In accordance with one embodiment of the present invention, thefirst ring is journalled on the secondary output shaft and the secondring is fixed to a rotary component of a transfer assembly driven by theprimary output shaft. Thus, the invention provides for installing thecontrollable, multi-mode, bi-directional overrunning clutch inassociation with the front output shaft to permit significant axiallength reductions for the transfer case.

[0009] In another embodiment, a first ring is driven by a first rotarycomponent, a second selectively sizable ring is non-rotatably coupled tothe first ring and a third split ring is journalled to a second rotarycomponent. A plurality of rollers are disposed within cam tracks formedin both the second and third rings. A modular construction is providedwhere the complex cam tracks are formed on a more easily manufacturedsecond ring instead of the first ring which typically includes a geartooth profile.

[0010] Thus, it is an object of the present invention to provide anon-demand transfer case equipped with a controllable, multi-mode,bi-directional overrunning clutch that advances the state of thefour-wheel drive technology.

[0011] It is a further object of the present invention to provide apower-operated actuator for controlling shifting of the clutch assemblybetween its distinct modes in response to mode signals received by acontroller unit.

[0012] Further objects, advantages and features of the present inventionwill become readily apparent to those skilled in the art by studying thefollowing description of the preferred embodiment in conjunction withthe appended drawings which are intended to set forth the best modecurrently contemplated for carrying out the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic view of a four-wheel drive motor vehicleequipped with a transfer case constructed according to the presentinvention;

[0014]FIG. 2 is a sectional view of the transfer case equipped with acontrollable, multi-mode, bi-directional overrunning clutch assembly andshift control system of the present invention;

[0015]FIG. 3 is a sectional view of the bi-directional overrunningclutch assembly shown in FIG. 2;

[0016]FIG. 4 is a rear end view of the bi-directional overrunning clutchassembly shown in FIG. 3;

[0017]FIG. 5 is similar to FIG. 4 except that the actuator ring has beenremoved from the clutch assembly;

[0018]FIG. 6 is a front end view of the clutch assembly;

[0019]FIG. 7 is a partial sectional view of the transfer case showingcomponents associated with the clutch actuator and the shift systemoperably located for establishing an on-demand four-wheel high-rangedrive mode;

[0020]FIG. 8 is similar to FIG. 7 but shows the components operablylocated to establish a part-time four-wheel high-range drive mode; and

[0021]FIGS. 9 and 10 are sectional views illustrating alternativeembodiments of the bi-directional overrunning clutch assembly inaccordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0022] Referring now to FIG. 1, a drive system 10 for a four-wheel drivemotor vehicle is shown to include a power source, such as engine 12,which drives a conventional transmission 14 of either the manually orautomatically shifted type. The output shaft of transmission 14 drivesan input member of a transfer case 16 which, in turn, delivers drivetorque to a primary output shaft 18 that is operably connected to aprimary driveline 20. Primary driveline 20 includes an axle assembly 22having a differential 24 driving a first pair of wheel assemblies 26 viaaxleshafts 28, and a drive shaft 30 connected between primary outputshaft 18 and differential 24. Transfer case 16 further includes asecondary output shaft 32 that is operably connected to a secondarydriveline 34. Secondary driveline 34 includes an axle assembly 36 havinga differential 38 driving a second pair of wheel assemblies 40 viaaxleshafts 42, and a driveshaft 44 connected between secondary outputshaft 32 and differential 38.

[0023] Drive system 10 also includes an electronic controller 48 whichreceives mode signals from a mode selector 46. Controller 48 receivesthe mode signals and generates control signals that are used to actuatea controllable shift system associated with transfer case 16. Accordingto the arrangement shown, primary driveline 20 is the rear driveline ofa rear wheel drive vehicle while secondary driveline 34 is its frontdriveline. However, it will be understood that the teachings of thepresent invention could easily be adapted for use in a front wheel drivevehicle in which the front driveline would be designated as the primarydriveline.

[0024] Referring primarily to FIG. 2, transfer case 16 is shown togenerally include an input shaft 50, rear output shaft 18, a planetaryreduction gearset 52, a range clutch 54, front output shaft 32, atransfer assembly 56, a bi-directional mode clutch assembly 58, and apower-operated shift system 60, all of which are mounted to a housingassembly 62. Input shaft 50 is adapted for direct connection to theoutput shaft of transmission 14. Planetary gearset 52 includes a sungear 64 fixed for rotation with input shaft 50, a ring gear 66non-rotatably fixed to housing assembly 62, and a plurality of planetgears 68 rotatably supported on a planet carrier 70. Range clutch 54includes a range collar 72 that is fixed via a splined connection 74 forrotation with and axial bi-directional movement on rear output shaft 18.Range collar 72 is moveable between a high-range (H) position, a neutral(N) position, and a low-range (L) position via axial translation of arange fork 76. In the H position, clutch teeth 78 on range collar 72engage. internal clutch teeth 80 on input shaft 50 so as to establish adirect ratio drive connection between input shaft 50 and rear outputshaft 18. In the L position, clutch teeth 78 on range collar 72 engageinternal clutch teeth 82 on planet carrier 70 so as to establish areduction ratio drive connection such that rear output shaft 18 isdriven at a reduced speed ratio relative to output shaft 18. In the Nposition, range collar 72 is disengaged from coupled engagement withboth input shaft 50 and planet carrier 70 such that no drive torque istransmitted from input shaft 50 to rear output shaft 18.

[0025] The position of range collar 72 and range fork 76 are controlledby a sector plate 86 and a power-operated actuator, such as an electricmotor/encoder assembly 88, that are associated with shift system 60.Sector plate 86 is rotated about an axis “A” by an output shaft 90 ofmotor assembly 88. Sector plate 86 has a contoured range slot 92 withinwhich a follower pin 94 is retained. Follower pin 94 is fixed to a shiftbracket 96 which is retained for sliding movement on a shift rail 98that is fixed to housing assembly 62. Range fork 76 has a C-shaped endsection retained in an annular groove formed in range collar 72. Abiasing spring 100 surrounds shift rail 98 and its opposite ends engagelaterally-spaced pairs of lugs 102 and 104 formed respectively onbracket 96 and range fork 76. As will be detailed, the contour of rangeslot 92 is configured to axially translate bracket 96 in response torotation of sector plate 86. Spring 100 functions as a resilient energystorage coupling between bracket 96 and range fork 76 that allows rapidand smooth engagement of clutch teeth 78 on range collar 72 with theclutch teeth 80 on input shaft 50 and clutch teeth 82 on planet carrier70 after a “block out” condition has been eliminated to complete theselected range shift.

[0026] It will be appreciated that planetary reduction gearset 52, rangecollar 72, range fork 76 and its corresponding connection to sectorplate 86, which function to provide a two-speed (i.e., high-range andlow-range) capability to transfer case 16 are optional such thattransfer case 16 could be functional as a one-speed direct drive unitequipped only with mode clutch assembly 58. Moreover, thenon-synchronized range shift system disclosed could alternatively bereplaced with a synchronized range shift system to permit “on-the-move”shifting between high and low-range without the need to stop thevehicle. Commonly-owned U.S. Pat. Nos. 5,911,644, 5,957,429, and6,056,666 disclose synchronized range shaft systems that are readilyadapted for use with transfer case 16 and which are hereby incorporatedby reference.

[0027] Transfer assembly 56 is driven by rear output shaft 18 and isshown to include a first sprocket 110 fixed via a splined connection 112to rear output shaft 18, a second sprocket 114 rotatably mounted onfront output shaft 32, and a power chain 116 meshed with both sprockets110 and 114. Mode clutch assembly 58 is provided for selectivelycoupling second sprocket 114 to front output shaft 32 for transferringdrive torque from rear output shaft 18 through transfer assembly 56 tofront output shaft 32. Clutch assembly 58 is a controllable, multi-mode,bi-directional overrunning clutch installed between second sprocket 114and front output shaft 32. Clutch assembly 58 includes an inner ring 118having an inner surface 120 concentrically mounted on an outer surface122 of front output shaft 32, and an outer ring 124 formed integrally asan axial hub extension of second sprocket 114. Inner ring, hereinafterreferred to as slipper ring 118, is a split ring having an actuationslot 125 defining a pair of first and second end surfaces 126 and 128,respectively. A series of axially-extending arcuate cam tracks 130 areformed in an outer surface of slipper ring 118 while a correspondingplurality of axially-extending arcuate cam tracks 132 are formed in aninner surface of outer ring 124. A like plurality of elongatedcylindrical rollers 134 are retained within aligned cam tracks 130 and132.

[0028] Clutch assembly 58 also includes a front end cap 136 and a rearend cap 138 that are oriented to enclose and retain rollers 134therebetween. Front end cap 136 has a plate segment that is fixed tosprocket 114 and an annular hub segment that is journalled on a portionof front output shaft 32. Rear end cap, hereinafter referred to asactuator ring 138, has a first cylindrical rim 140 and a secondcylindrical rim 142 interconnected by a plurality of radial web segments144 so as to define elongated arcuate cut-outs 146 therebetween. Secondrim 142 is aligned with one end of rollers 134 while thickened portions140A of first rim 140, which are aligned with web segments 144, arejournalled on an outer surface 148 of outer ring 124. A radial lug 150formed integrally with one of web segments 144 is retained in actuationslot 125 of slipper ring 118. Actuator ring 138 also includes a thirdcylindrical rim 152 extending rearwardly from a radial flange 154.Actuator ring 138 is preferably made from brass and is retained in itsassembled position relative to front output shaft 32 via a thrust washer156 and a snap ring 158. Bearing assemblies 160 and 162 are shown torotatably support front output shaft 32 in housing 62.

[0029] Clutch assembly 58 further includes a drag band 164 shown whichencircles third rim 152 of actuator ring 138 and which has a pair ofends 166 and 168 (see FIGS. 7 and 8). A roll pin 169 and a spring (notshown) interconnect ends 166 and 168 to ensure that drag band 164normally maintains a predetermined drag force on third rim 152 ofactuator ring 138. Drag band 164 is preferably made of brass or asuitable spring material.

[0030] Mode clutch assembly 58 is controlled by power-operated shiftsystem 60 in response to the mode signal sent to controller 48 by modeselector 46. As will be detailed, sector plate 86 is rotated by electricmotor assembly 88 to move a mode fork 172 for shifting mode clutchassembly 58 between an on-demand four-wheel drive mode and a locked orpart-time four-wheel drive mode. As best seen from FIG. 7 and 8, a camrod segment 170 of mode fork 172 is disposed between ends 166 and 168 ofdrag band 164 and a circlip 174 is provided for biasing band ends 166and 168 into contact with opposite edge surfaces of cam rod segment 170.Mode fork 172 is shown in FIG. 2 to include a cylindrical hub segment176 that is journalled on shift rail 98 for axial bi-directionalmovement thereon. A return spring 178 surrounds shift rail 98 and actsbetween mode fork 172 and housing 62 for biasing a follower segment 180of mode fork 172 into continuous engagement with a contoured cammingedge 182 of sector plate 86. The contour of camming edge 182 functionsto cause mode fork 172 to move between first and second mode positionsin response to rotation of sector plate 86. Thus, rotation of sectorplate 86 controls coordinated axial movement of range fork 76 and modefork 172 to establish a plurality of distinct combinations of drivemodes and speed ranges.

[0031] According to a preferred embodiment of the present invention,sector plate 86 may be rotated to any one of five distinct sectorpositions to establish a corresponding number of drive modes. Thesedrive modes include a part-time four-wheel high-range drive mode, anon-demand four-wheel high-range drive mode, a neutral mode, a part-timefour-wheel low-range drive mode, and an on-demand four-wheel low-rangedrive mode. The particular four-wheel drive mode selected is establishedby the position of mode fork 172 and range fork 76. In operation, thevehicle operator selects a desired drive mode via actuation of modeselector 46 which, in turn, sends a mode signal to controller 48 that isindicative of the particular drive mode selected. Thereafter, controller48 generates an electric control signal that is applied to motorassembly 88 for controlling the rotated position of sector plate 86.

[0032] Mode selector 46 can take the form of any mode selector devicewhich is under the control of the vehicle operator for generating a modesignal indicative of the specific mode selected. In one form, the modeselector device may be in an array of dash-mounted push button switches.Alternatively, the mode selector may be a manually-operable shift leversequentially moveable between a plurality of positions corresponding tothe available operational modes which, in conjunction with a suitableelectrical switch arrangement, generates a mode signal indicating theselected mode. In either form, mode selector 46 offers the vehicleoperator the option of deliberately choosing between the variousoperative drive modes.

[0033] Referring again to FIGS. 7 and 8, sector plate 86 is shown tohave five distinct detent positions labeled 4H-LOCK, 4H-AUTO, N, 4L-LOCKand 4L-AUTO. Each detent position corresponds to an available drive modethat can be selected via mode selector 46. In particular, FIG. 7illustrates a poppet assembly 188 retained in the 4H-LOCK detent ofsector plate 86 which represents establishment of the part-timefour-wheel high-range drive mode wherein range collar 72 is located inits H position and mode fork 172 is located in its first mode position.With mode fork 172 in its first mode position, the profile of ahigh-range segment 182 a of camming edge 182 has forced cam rod segment170 to move to a first position, in opposition to the biasing of spring178. In this first position, ends 166 and 168 of drag band 164 have beenforcibly separated so as to engage the side surfaces of a widerintermediate portion 170 a of cam rod segment 170. Such separation ofends 166 and 168 of drag band 164 acts to release the circumferentialdrag force normally exerted on actuator ring 138.

[0034] With drag band 164 released from frictional engagement with thirdrim 152 of actuator ring 138 due to movement of cam rod segment 170 toits first position, radial lug 150 is initially positioned centrally inactuation slot 125 of slipper ring 118, as shown in FIG. 4. Whencentrally located, the opposite edges of lug 150 are displaced from endsurfaces 126 and 128 of actuation slot 125. As such, relative rotationbetween front output shaft 32 and rear output shaft 18 in eitherdirection (i.e., front overrunning rear or rear overrunning front)causes a limited amount of relative rotation between slipper ring 118and outer ring 124. Such limited relative movement causes rollers 134 toride up the circumferentially indexed cam tracks 130 and 132 which, inturn, causes rollers 134 to exert a radially inwardly directedfrictional locking force on slipper ring 118, thereby clamping innersurface 120 of slipper ring 118 to outer surface 122 of front outputshaft 32. Accordingly, mode clutch assembly 58 is locked and secondsprocket 114 is coupled to front output shaft 32 such that drive torqueis transferred from rear output shaft 18 through transfer assembly 56 tofront output shaft 32. In effect, front output shaft 32 is coupled torear output shaft 18 to establish the part-time four-wheel drive mode.

[0035] Referring to FIG. 8, poppet assembly 188 is shown retained in the4H-AUTO detent which represents establishment of the on-demandfour-wheel high-range drive mode wherein range collar 72 is stilllocated in its H position and mode fork 172 has moved from its firstmode position (FIG. 7) to its second mode position in response torotation of sector plate 86. A high-range dwell section 92 a of rangeslot 92 maintains follower 94 at the same axial location along shiftrail 98 during rotation of sector plate 86 in the clockwise directionfrom the 4H-LOCK position to the 4H-AUTO position, thereby maintainingrange collar 72 in its H position. With mode fork 172 in its second modeposition, the tapered profile of high-range segment 182 a of cammingedge 182 acts to locate cam rod segment 170 in a second position suchthat ends 166 and 168 of drag band 164 now engage a thinner terminal endportion 170 b of cam rod segment 170. Contraction of the distancebetween ends 166 and 168 of drag band 164 acts to re-engage thecircumferential drag force exerted by drag band 164 on third rim 152 ofactuator ring 138. Therefore, initial rotation of rear output shaft 18and front output shaft 32 caused by motive operation of the vehicleresults in circumferential indexing of actuator ring 138 relative tosecond sprocket 114 until lug 150 engages one of end surfaces 126 and128 of actuation slot 125 in slipper ring 118.

[0036] For example, if the vehicle is rolling forward, second sprocket114 would rotate counter clockwise (see FIG. 4) and the drag exerted bydrag band 164 would cause actuator ring 138 to index in a clockwisedirection until lug 150 engages end surface 128. In this position, lug150 prevents rotation of slipper ring 118 in a first direction (i.e.,counter-clockwise) relative to outer ring 124 while permitting limitedrotation of slipper ring 118 in a second direction (i.e., clockwise)relative to outer ring 124. Since outer ring 124 is driven by rearoutput shaft 18 via transfer assembly 56, and slipper ring 118 ismounted on front output shaft 32, mode clutch assembly 58 is maintainedin an unlocked condition during relative rotation in the first directionand automatically locks in response to relative rotation in the seconddirection. Specifically, with lug 150 engaging end surface 128 ofslipper ring 118 it acts to maintain alignment between slipper ring 118and outer ring 124 with rollers 134 centrally located in cam tracks 130and 132. As such, slipper ring 118 is not frictionally clamped to frontoutput shaft 32 and front output shaft 32 is allowed to overrun rearoutput shaft 18.

[0037] However, if traction is lost at rear wheels 26 and rear outputshaft 18 attempts to overrun front output shaft 32, slipper ring 118moves in the second direction relative to outer ring 124. This limitedrelative rotation causes rollers 134 to ride up cam tracks 130 and 132which acts to frictionally clamp slipper ring 118 to front output shaft32, thereby locking mode clutch assembly 58 for transferring drivetorque from rear output shaft 18 through transfer assembly 56 and modeclutch assembly 58 to front output shaft 32. This one-way lockingfunction automatically establishes the on-demand four-wheel high-rangedrive mode during forward motion of the vehicle since front output shaft32 is coupled for rotation with rear output shaft 18. However, once thetraction loss condition has been eliminated, actuator ring 138 againindexes in a clockwise direction until lug 150 re-engages end surface128 of slipper ring 118. Thus, mode clutch assembly 58 is released andautomatically returns to operation in its unlocked mode. Namely, oncethe rear wheel slip has been eliminated, slipper ring 118 moves relativeto outer ring 124 for again locating rollers 134 centrally in cam tracks130 and 132 to disengage mode clutch assembly 58 until the next losttraction situation occurs.

[0038] During reverse motive operation of the vehicle in the on-demandfour-wheel drive mode, second sprocket 114 would rotate clockwise (FIG.4) and the drag force would cause actuator ring 138 to circumferentiallyindex until lug 150 is located adjacent to end surface 126 of slipperring 118. This arrangement is the reverse of that described for forwardoperation such that limited relative rotation is permitted betweenslipper ring 118 and outer ring 124 in the first direction but preventedin the second direction. Thus, operation in the on-demand four-wheeldrive mode during reverse travel of the vehicle also permits frontoutput shaft 32 to overrun rear output shat 18 during tight corneringwhile mode clutch assembly 58 locks to transfer drive torque to frontoutput shaft 32 during lost traction at the rear wheels. As such, oncethe on-demand four-wheel high-range drive mode is established, it isoperational during both forward and reverse travel of the vehicle. Thus,when transfer case 16 functions in its on-demand mode, it permits frontdrive shaft 44 to overrun rear drive shaft 30 with all drive torquedelivered to rear driveline 20. Drive torque is only transferred tofront driveline 34 through mode clutch assembly 58 when rear outputshaft 18 attempts to overrun front output shaft 32.

[0039] When it is desired to shift transfer case 16 from its on-demandfour-wheel high-range drive mode into its neutral mode, the mode signalfrom mode selector 46 is sent to controller 48 which then sends acontrol signal to electric motor 88 to rotate sector plate 86 clockwiseuntil poppet assembly 188 is located in its N detent. Such rotation ofsector plate 86 causes range follower 94 to exit high-range dwellsection 92 a of range slot 92 and travel within a shift section 92 bthereof. The contour of shift section 92 b causes range fork 76 to moveaxially which causes corresponding movement of range collar 72 from itsH position to its N position. Concurrently, follower segment 180 of modefork 172 exits high-range segment 182 a of camming edge 182 and travelsalong a dwell segment 182 b thereof which is contoured to maintain modefork 172 in its second mode position.

[0040] When mode selector 46 indicates selection of the part-timefour-wheel low-range drive mode, sector plate 86 is rotated until poppetassembly 188 is located in the 4L-LOCK detent. Assuming the shiftsequence required continued rotation of sector plate 86 in the clockwisedirection. range follower 94 continues to travel within shift section 92b of range slot 92 which acts to axially move range collar 72 from its Nposition to its L position. Concurrently, mode follower segment 180exits dwell segment 182 b of camming edge 182 and travels along alow-range segment 182 c which functions to move mode fork 172 from itssecond mode position into its first mode position. As previouslydescribed, locating mode fork 172 in its first mode position causes abi-directional locking of mode clutch assembly 58 for establishing thepart-time four-wheel low-range drive mode.

[0041] Upon selection of the on-demand four-wheel low-range drive mode,sector plate 86 is rotated by electric motor assembly 88 until poppetassembly 188 is located in its 4L-AUTO detent. Such rotation of sectorplate 86 causes range follower 94 to travel within a low-range dwellsection 92 c of range slot 92 so as to maintain range collar 72 in its Lposition. Such rotation of sector plate 86 also causes follower segment180 of mode fork 172 to ride against a cam segment 18 d of camming edge182 which forcibly urges mode fork 172 to move from its first positionto its second mode position. Thus, the on-demand four-wheel low-rangedrive mode is established when range fork is in its L position and modefork 172 is in its second mode position. The automatic operation of modeclutch assembly 58 described above in reference to the on-demandhigh-range drive mode is identical to that provided in the on-demandfour-wheel low-range drive mode.

[0042] An alternate embodiment of a mode clutch assembly 200 is depictedin FIG. 9. Clutch assembly 200 functions substantially identically toclutch assembly 58 in that it is a controllable, multi-mode,bi-directional overrunning clutch. Additionally, clutch assembly 200addresses the need for a cost effective design that may be used for avariety of traction control systems. To construct clutch assembly 58, asdescribed in FIG. 2, special machining of outer ring 124 in secondsprocket 114 is required to form arcuate cam tracks 132. In order tosimplify machining of sprocket 114, clutch assembly 200 now incorporatesa tubular sleeve, hereinafter referred to as intermediate ring 202,which includes a series of axially-extending arcuate cam tracks 204formed on its inner surface. This tubular insert design allows formodular construction of a bi-directional overrunning clutch assemblythat can be easily configured for use in different applications.Specifically, a number of differently sized shafts and sprockets may beinterconnected via a standardized clutch assembly through the use of anintermediate ring 202 having a thickness 206 selected to account fordifferent clearances between the sprocket and the shaft. As such, a setof intermediate rings 202 having different thicknesses can be used todrivingly interconnect a number of shafts and sprocket combinations,thereby reducing the overall cost of the product line.

[0043] As stated, clutch assembly 200 is substantially similar instructure and function to that of clutch assembly 58. As such, commonelements will retain the reference numerals previously introduced.Furthermore, it should be appreciated that while clutch assembly 200 isdepicted as selectively interconnecting a driven second sprocket 208 tofront output shaft 32, clutch assembly 200 may, in the alternative, bepositioned to selectively couple first sprocket 110 to rear output shaft18, or to selectively couple any other pair of rotary components.

[0044] With continued reference to FIG. 9, clutch assembly 200 is shownto include an inner ring or slipper ring 118 having inner surface 120concentrically mounted on outer surface 122 of front output shaft 32.Intermediate ring 202 is non-rotatably coupled to an outer ring 212.Outer ring 212 is preferably formed as an axial hub extension of secondsprocket 208 and defines a cylindrical chamber within which intermediatering 202 is disposed. Preferably, intermediate ring 202 is coupled tosecond sprocket 208 with a light interference fit between itscylindrical outer surface 213 and a cylindrical inner surface 214 of thechamber formed in second sprocket 208. If desired, the end ofintermediate ring 202 can be secured to sprocket 208 via a secondaryoperation (i.e., welding, staking, etc.). In addition, the generallythin-walled construction of intermediate ring 202 will allow its surface213 to expand and further engage inner surface 214 of second sprocket208 when a radial separating force is generated by rollers 134 duringlocking actuation of clutch assembly 200. This feature eliminates theneed for a torque driving mechanism such as, for example, a spline or akey to be used to secure intermediate ring 202 to outer ring 212.

[0045] Furthermore, it should be appreciated that the modularintermediate ring and sprocket design permits the use of minimallycomplex machining processes to provide consistent size, shape andlocation of cam tracks 204. Intermediate ring 202 may be formed usingcommon processes such as finish turning of a blank or a bar. Forexample, a die-set cam broaching process with a wafer type expandablemandrel can be performed prior to heat treatment to form the inner camtracks in intermediate ring 202. Hardening is achieved by induction heattreatment and die quenching. Grinding or hard turning may be used tofinish the outside diameter of intermediate ring 202 to maintain orestablish alignment with the internal cam tracks.

[0046] As noted, second sprocket 208 is manufactured With a smoothcylindrical inner surface 214. This design permits standard machiningand finishing processes to be utilized. If desirable, a radiallyinwardly extending lip 216 can be formed to provide a seat 218 for anend surface 220 of intermediate ring 202. During assembly, intermediatering 202 is located via a positive stop when end surface 220 engagesseat 218. The remaining components not specifically described inrelation to clutch assembly 200 function substantially similarly to thecomponents of clutch assembly 58.

[0047]FIG. 10 depicts another alternate mode clutch assembly 300. Clutchassembly 300 is substantially similar to clutch assembly 200 except thata tubular sleeve, referred to as intermediate ring 302, is non-rotatablycoupled to a front output shaft 304. Intermediate ring 302 includes asubstantially smooth cylindrical inner surface 306 and an outer surfaceformed to include a plurality of axially-extending arcuate cam tracks308. Inner surface 306 is secured via a light press fit to cylindricalouter surface 122 of front output shaft 32. In addition, a slipper ring310 is provided which has an inner surface formed to include acorresponding plurality of axially-extending arcuate cam tracks 312.Cylindrical rollers 134 are retained within aligned cam tracks 308 and312. Upon locking of mode clutch assembly 300, an outer surface 314 ofslipper ring 310 is frictionally engaged with an inner surface 316 of adriven second sprocket 318.

[0048] An actuator ring 320 is provided includes a radial lug 322.Slipper 310 is a split ring having an actuation slot (not shown). Lug322 is positioned within the actuation slot. Therefore, clutch assembly300 may be actuated by controlling rotation of actuator ring 320relative to slipper ring 310, thereby causing slipper ring 310 to rotaterelative to intermediate ring 302. Based on the geometry of cam tracks308, 312 and rollers 134, slipper ring 310 will frictionally engageinner surface 316 of second sprocket 318 upon selective rotation ofactuator ring 320.

[0049] The present invention provides an efficient arrangement forshifting a multi-mode bi-directional clutch assembly in a power transferunit, such as a four-wheel drive transfer case.

[0050] Preferred embodiments have been disclosed to provide thoseskilled in the art an understanding of the best mode currentlycontemplated for the operation and construction of the presentinvention. The invention being thus described, it will be obvious thatvarious modifications can be made without departing from the true spiritand scope of the invention, and all such modifications as would beconsidered by those skilled in the art are intended to be includedwithin the scope of the following claims.

What is claimed is:
 1. A power transmission device comprising: a rotaryinput member adapted to receive drive torque from a source of torque; arotary output member adapted to provide drive torque to an outputdevice; and a torque transfer mechanism operable for transferring drivetorque from said input member to said output member, said torquetransfer mechanism including a bi-directional overrunning clutch havinga first ring non-rotatably coupled to one of said rotary input memberand said rotary output member, a second ring spaced apart from the otherof said rotary input member and said rotary output member and rollersdisposed in aligned cam tracks formed in facing surfaces of said firstand second rings, said second ring adapted to circumferentially indexrelative to said first ring to cause said rollers to ride up said camtracks and cause said second ring to frictionally engage the other ofsaid rotary input member and said rotary output member.
 2. The powertransmission device of claim 1 wherein said rotary input member includesa substantially cylindrical bore, and wherein said first ring has anouter surface engaging said bore and an inner surface on which said camtracks are formed.
 3. The power transmission device of claim 2 whereinsaid first ring includes a thickness between its outer surface and itsinner surface, and wherein said thickness is varied to account forvaried spacing between said bore and said rotary output member.
 4. Thepower transmission device of claim 3 wherein said rotary input memberincludes an annular lip inwardly protruding from said bore, and whereinsaid first ring includes an end face engaging said lip.
 5. The powertransmission device of claim 1 wherein said second ring is a split ringdefining an actuation slot having first and second edge surfaces, saidpower transmission device further including an actuator ring having alug retained in said actuation slot of said split ring and which ismoveable from a central position disengaged from said first and secondedge surfaces in a first direction into engagement with said first edgesurface and in a second direction into engagement with said second edgesurface.
 6. The power transmission device of claim 5 wherein saidactuator ring has a rim on which a drag band is retained, said drag bandhaving a pair of ends between which a cam member is retained, said cammember having a first segment operable to cause said drag band to exerta drag force on said rim of said actuation ring which causescircumferential indexing of said actuator ring in response to relativerotation between said first and second rings, said cam member furtherincluding a second segment operable to release said drag force from saidactuation ring.
 7. A power transmission device comprising: a rotaryinput member adapted to receive drive torque from a source of torque; arotary output member adapted to provide drive torque to an outputdevice; and a torque transfer mechanism operable for transferring drivetorque from said input member to said output member, said torquetransfer mechanism including a bi-directional overrunning mode clutchhaving a first ring driven by said rotary input member, a second ringnon-rotatably coupled to said first ring, a third ring positioned onsaid rotary output member and rollers disposed in aligned cam tracksformed in facing surfaces of said second and third rings, said thirdring adapted to circumferentially index relative to said second ring tocause said rollers to ride up said cam tracks and cause-said third ringto frictionally engage said rotary output member, and a mode actuatorthat is moveable between a first position and a second position toestablish corresponding AUTO and LOCK modes, said overrunning clutchbeing operable in its AUTO mode to permit relative rotation between saidrotary input member and said rotary output member in a first directionand prevent relative rotation therebetween in a second direction, andsaid overrunning clutch being operable in its LOCK mode to preventrelative rotation between said rotary input member and said rotaryoutput member in both directions.
 8. The power transmission device ofclaim 7 wherein said first ring includes a substantially cylindricalbore, and wherein said second ring has an outer surface engaging saidbore and an inner surface on which said cam tracks are formed.
 9. Thepower transmission device of claim 8 wherein said second ring has athickness defined between its inner and outer surfaces and wherein saidthickness is varied to account for varied spacing between said bore andsaid rotary output member.
 10. The power transmission device of claim 9wherein said first ring includes an annular lip protruding from saidbore and said second ring includes an end surface engaging said lip. 11.The power transmission device of claim 7 wherein said third ringincludes an actuation slot having first and second edge surfaces, andwherein said mode actuator is an actuator ring having a lug retained insaid actuation slot of said third ring and which is moveable from acentral position disengaged from said first and second edge surfaces ina first direction into engagement with said first edge surface and in asecond direction into engagement with said second edge surface.
 12. Thepower transmission device of claim 11 wherein said actuator ring has arim on which a drag band is retained, said drag band having a pair ofends between which a cam member is retained, said cam member having afirst segment operable to cause said drag band to exert a drag force onsaid rim of said actuation ring which causes circumferential indexing ofsaid actuator ring in response to relative rotation between said secondand third rings, said cam member further including a second segmentoperable to release said drag force from said actuation ring.
 13. Apower transmission device comprising: a rotary input member adapted toreceive drive torque from a source of torque; a rotary output memberadapted to provide drive torque to an output device; and abi-directional overrunning clutch operable for transferring drive torquefrom said input member to said output member, said bi-directionaloverrunning clutch including a first ring driven by said rotary outputmember, a second ring non-rotatably coupled to said rotary input member,a third ring positioned between said first ring and said second ring androllers disposed in aligned cam tracks formed in facing surfaces of saidsecond and third rings, said third ring adapted to circumferentiallyindex relative to said second ring to cause said rollers to ride up saidcam tracks and cause said third ring to frictionally engage said firstring.
 14. The power transmission device of claim 13 further including anactuator for controlling rotational movement of said third ring relativeto said second ring.
 15. The power transmission device of claim 14wherein the actuator is moveable between a first position and a secondposition to establish corresponding AUTO and LOCK modes, said powertransmission device being operable in its AUTO mode to permit relativerotation between said rotary input member and said rotary output memberin a first direction and prevent relative rotation therebetween in asecond direction, and said power transmission device being operable inits LOCK mode to prevent relative rotation between said rotary inputmember and said rotary output member in both directions.
 16. The powertransmission device of claim 15 wherein said power transmission deviceis a transfer case with said rotary input member being a first outputshaft and said rotary output member being a second output shaft.
 17. Apower transmission coupling comprising: a first coupling memberincluding a first friction surface; a second coupling member including afirst cylindrical bearing surface; a third coupling member including asecond cylindrical bearing surface and a third cylindrical bearingsurface, said third bearing surface including a plurality of firstrecesses; a tubular slipper positioned between said first and thirdcoupling members, said tubular slipper including a second frictionsurface for engagement with said first friction surface, and a fourthcylindrical bearing surface including a plurality of second recesses,each of said first recesses together with their respective one of saidsecond recesses defining a pocket; a plurality of roller elementsdisposed in said pockets for coupling said first coupling member to saidsecond coupling member when said tubular slipper and said third couplingmember rotate relative to one another; and an actuator for controllingrotational movement of said tubular slipper relative to said thirdcoupling member.
 18. The power transmission coupling of claim 17 whereinthe actuator is moveable between a first position and a second positionto establish corresponding AUTO and LOCK modes, said power transmissiondevice being operable in its AUTO mode to permit relative rotationbetween said first coupling member and said third coupling member in afirst direction and prevent relative rotation therebetween in a seconddirection, and said power transmission device being operable in its LOCKmode to prevent relative rotation between said first coupling member andsaid third coupling member in both directions.
 19. The powertransmission coupling of claim 18 wherein each of said first, second,third and fourth cylindrical bearing surfaces are substantiallycoaxially aligned.
 20. The power transmission coupling of claim 17wherein the power transmission coupling is located within a transfercase.
 21. The power transmission coupling of claim 17 wherein saidtubular slipper is a split ring defining an actuation slot having firstand second edge surfaces, said actuator including an actuator ringhaving a lug retained in said actuation slot of said split ring andwhich is moveable from a central position disengaged from said first andsecond edge surfaces in a first direction into engagement with saidfirst edge surface and in a second direction into engagement with saidsecond edge surface.
 22. The power transmission coupling of claim 17wherein said first coupling member is selected from the group consistingof a rotary shaft and a sprocket.
 23. A method of making a powertransmission device comprising: determining a distance between a firstbearing surface of a first coupling member and a first friction surfaceof a second coupling member; selecting a third coupling member from agroup of coupling members having different thicknesses, said selectionbeing based on said distance, said third coupling member including asecond bearing surface and a third bearing surface; engaging said firstbearing surface with said second bearing surface to non-rotatably couplesaid third coupling member to said first coupling member; positioning aplurality of rollers between said third coupling member and a tubularslipper, said tubular slipper having a second friction surface and afourth bearing surface, said third and fourth bearing surfaces havingcam tracks formed thereon to receive said plurality of rollers; andpositioning said second friction surface spaced apart from said firstfriction surface to allow selective coupling of said first couplingmember and said second coupling member by rotating said tubular slipperrelative to said third coupling member.
 24. The method of claim 23further including coaxially aligning cylinders defined by each of saidfirst bearing surface, said second bearing surface, said third bearingsurface, said fourth bearing surface, said first friction surface andsaid second friction surface.
 25. The method of claim 23 wherein saidfirst coupling member is a sprocket having teeth engaging a powertransfer element.
 26. The method of claim 23 wherein said first couplingmember is a rotary shaft.
 27. The method of claim 23 further includingengaging an edge of said third coupling member with a lip radiallyinwardly extending from said first coupling member.
 28. A transfer casefor transferring drive torque from a powertrain to first and seconddrivelines of a motor vehicle, said transfer case comprising: a firstshaft adapted to transfer drive torque from the powertrain to the firstdriveline; a second shaft adapted for connection to the seconddriveline; a transfer assembly including a first sprocket driven by saidfirst shaft, a second sprocket surrounding said second shaft, and adrive mechanism interconnecting said second sprocket to said firstsprocket; and a mode clutch for selectively coupling said second shaftfor rotation with said second sprocket, said mode clutch including afirst ring having an outer surface engaging an inner surface of saidsecond sprocket and an inner surface with first cam surfaces, a secondring having an inner surface mounted on an outer surface of said secondshaft and an outer surface with second cam surfaces, and rollersdisposed between aligned sets of said first and second cam surfaces,said second ring adapted to circumferentially index relative to saidfirst ring to cause said rollers to ride up said cam surfaces and causesaid inner surface of said second ring to frictionally engage said outersurface of said second shaft.
 29. The transfer case of claim 28 furthercomprising: an actuator that is moveable between first and secondpositions to establish corresponding AUTO and LOCK modes for said modeclutch, said mode clutch is operable in its AUTO mode to permit relativerotation between said first and second shafts in a first direction andprevent relative rotation therebetween in a second direction, and saidmode clutch is operable in its LOCK mode to prevent relative rotationbetween said first and second shafts in both directions; and a shiftmechanism for moving said actuator between its first and secondpositions.
 30. A transfer case for transferring drive torque from apowertrain to first and second drivelines of a motor vehicle, saidtransfer case comprising: a first shaft adapted to transfer drive torquefrom the powertrain to the first driveline; a second shaft adapted forconnection to the second driveline; a transfer assembly including afirst sprocket surrounding said first shaft, a second sprocket fixed tosaid second shaft, and a drive mechanism interconnecting said firstsprocket to said second sprocket; and a mode clutch for selectivelycoupling said first sprocket for rotation with said first shaft, saidmode clutch including a first ring having an outer surface engaging aninner surface of said first sprocket and an inner surface with first camsurfaces, a second ring having an inner surface mounted on an outersurface of said first shaft and an outer surface with second camsurfaces, and rollers disposed between aligned sets of said first andsecond cam surfaces, said second ring adapted to circumferentially indexrelative to said first ring to cause said rollers to ride up said camsurfaces and cause said inner surface of said second ring tofrictionally engage said outer surface of said first shaft.
 31. Thetransfer case of claim 30 further comprising: an actuator that ismoveable between first and second positions to establish correspondingAUTO and LOCK modes for said mode clutch, said mode clutch is operablein its AUTO mode to permit relative rotation between said first andsecond shafts in a first direction and prevent relative rotationtherebetween in a second direction, and said mode clutch is operable inits LOCK mode to prevent relative rotation between said first and secondshafts in both directions; and a shift mechanism for moving saidactuator between its first and second positions.
 32. A transfer case fortransferring drive torque from a powertrain to first and seconddrivelines of a motor vehicle, said transfer case comprising: a firstshaft adapted to transfer drive torque from the powertrain to the firstdriveline; a second shaft adapted for connection to the seconddriveline; a transfer assembly including a first sprocket driven by saidfirst shaft, a second sprocket surrounding said second shaft, and adrive mechanism interconnecting said second sprocket to said firstsprocket; and a mode clutch for selectively coupling said second shaftfor rotation with said second sprocket, said mode clutch including afirst ring having an outer surface engageable with an inner surface ofsaid second sprocket and an inner surface with first cam surfaces, asecond ring having an inner surface secured to an outer surface of saidsecond output shaft and an outer surface with second cam surfaces, androllers disposed between aligned sets of said first and second camsurfaces, said first ring adapted to circumferentially index relative tosaid second ring to cause said rollers to ride up said cam surfaces andcause said outer surface of said first ring to frictionally engage saidinner surface of said second sprocket.
 33. The transfer case of claim 32further comprising: an actuator that is moveable between first andsecond positions to establish corresponding AUTO and LOCK modes for saidmode clutch, said mode clutch is operable in its AUTO mode to permitrelative rotation between said first and second shafts in a firstdirection and prevent relative rotation therebetween in a seconddirection, and said mode clutch is operable in its LOCK mode to preventrelative rotation between said first and second shafts in bothdirections; and a shift mechanism for moving said actuator between itsfirst and second positions.
 34. A transfer case for transferring drivetorque from a powertrain to first and second drivelines of a motorvehicle, said transfer case comprising: a first shaft adapted totransfer drive torque from the powertrain to the first driveline; asecond shaft adapted for connection to the second driveline; a transferassembly including a first sprocket surrounding said first shaft, asecond sprocket fixed to said second shaft, and a drive mechanisminterconnecting said second sprocket to said first sprocket; and a modeclutch for selectively coupling said first sprocket for rotation withsaid first shaft, said mode clutch including a first ring having anouter surface engageable with an inner surface of said first secondsprocket and an inner surface with first cam surfaces, a second ringhaving an inner surface secured to an outer surface of said secondoutput shaft and an outer surface having second cam surfaces, androllers disposed between aligned sets of said first and second camsurfaces, said first ring adapted to circumferentially index relative tosaid second ring to cause said rollers to ride up said cam surfaces andcause said outer surface of said first ring to frictionally engage saidinner surface of said first sprocket.
 35. The transfer case of claim 34further comprising: an actuator that is moveable between first andsecond positions to establish corresponding AUTO and LOCK modes for saidmode clutch, said mode clutch is operable in its AUTO mode to permitrelative rotation between said first and second shafts in a firstdirection and prevent relative rotation therebetween in a seconddirection, and said mode clutch is operable in its LOCK mode to preventrelative rotation between said first and second shafts in bothdirections; and a shift mechanism for moving said actuator between itsfirst and second positions.